Reinforced thin wall thermoplastic storage vessel manufacture

ABSTRACT

A method and apparatus is disclosed for reinforcement of a thin wall hollow thermoplastic storage vessel with one or more wraps of continuous fibers. This method requires thermal bonding between the reinforcement fibers and the outer surface of the thermoplastic storage vessel while the interior cavity of the storage vessel is being pressurized. The fiber wraps can also be oriented in spatial directions further resisting internal stress on the storage vessel walls when put into service.

[0001] This is a continuation in part of application Ser. No.10/267,723, filed Oct. 10, 2002 and now abandoned.

BACKGROUND OF THE INVENTION

[0002] This invention relates generally to a method for reinforcement ofhollow thermoplastic storage vessels with one or more wraps ofcontinuous fibers and more particularly to a means for improved bondingbetween the applied fibers and the outer vessel surface for storagevessels having relatively thin walls.

[0003] In a co-pending application Ser. No. 09/327,003 entitled“Reinforced Thermoplastic Pipe Coupling” and filed Jun. 7, 1999 in thenames of David E. Hauber, Robert J. Langone and James A. Mondo which isnow U.S. Pat. No. 6,164,702 and also assigned to the present assignee,there is disclosed a continuous fiber reinforced thermoplastic pipecoupling having improved resistance to applied stress when used withpipe lengths being joined together. The fiber reinforcement is alignedduring placement in a particular manner and placed at predeterminedfiber angles dictated by mechanical forces being applied such as byinternal fluid pressure in the coupled pipe lengths. Said already knownmethod for construction of said reinforced thermoplastic pipe couplingincludes a controlled directional orientation of the fiber component toenable the fiber placement to be fixed for maximum effectiveness inwithstanding the particular stress being generated when the joinedtogether pipe lengths are customarily used for the transfer ofpressurized fluids. Since the fiber materials currently used in thismanner are generally stronger than the polymer matrix compositions nowalso being employed, the overall strength produced in the compositemember depends largely upon the fiber placement direction for theparticular end product. The fiber reinforced coupler is thereby only asstrong as the spatial direction of the included fibers with respect tothe direction of the internal stress when applied to said member. Thus,when the fiber reinforced coupler is stressed by internal fluid pressurein the direction of the fiber placement, the applied load is withstoodprimarily by the included fibers and the coupler strength in resistingsuch stress is at a maximum value. Conversely, when the composite memberis stressed in a perpendicular direction to the fiber direction, theapplied force must necessarily be resisted primarily by the polymermatrix so that the coupler strength is at minimum. The relative amountsof the individual stresses being applied to the fiber reinforced couplermust also necessarily be considered for proper fiber placementdirection. For an externally unconstrained installation of saidpreviously disclosed pipe couplings, such as encountered with the aboveground pipe installations, the applied loads can be examined by treatingthe joined pipe lengths as a pressure vessel. From such analysis it wasfound that the stress applied to the pipe wall in the hoop direction istwice an amount as the applied stress in the pipe's axial direction.Employing well recognized shell theory calculation, it was further foundthat a fiber angle of 55 degrees was needed to balance these appliedloads assuming 90 degrees to be in the pipe hoop direction and 0 degreesto be aligned in the direction of the pipe longitudinal axis. Forconstrained pipe installations, however, such as in-ground or having thepipe ends being held there, there can only be need for resisting hoopstress. Accordingly, fiber placement at or near a 90 degree angle withrespect to the longitudinal pipe axis was dictated while furtherrecognizing that some angle less than 90 degrees may only be achievablewith the fiber winding in the customary manner. The entire contents ofsaid referenced co-pending application are hereby specificallyincorporated into the present application.

[0004] It can readily be appreciated that thermoplastic storage vesselsundergo similar internal stress when being utilized. Accordingly, theeffectiveness of fiber reinforcement for thermoplastic storage vesselwill also depend to a considerable degree upon the same factorspreviously considered with respect to said reinforced thermoplasticcouplings. For example, a thermoplastic storage vessel having acylindrical configuration can generally have the fiber wraps applied ina hoop direction for maximum reinforcement whereas a spherical storagevessel will understandably have the fiber placement angle varied indifferent spatial directions. It has now been found, however, thatthermal bonding the reinforcement fibers to the outer surface of thethermoplastic storage vessel in the same manner previously employed forreinforcement of said thermoplastic pipe couplings produces inferiorresults. Specifically, the previously employed bonding method providedsufficient thermal expansion of the thermoplastic inner coupling memberwhen being carried out that an effective thermal bonding with theapplied fiber replacement took place. This does not reliably occur forvarious shaped thermoplastic storage vessels having a lesser wallthickness. It thereby becomes necessary for said relatively thin wallstorage vessels to adopt an improved thermal bonding procedure for thefiber reinforcement to have the desired effectiveness.

[0005] It is an important object of the present invention, therefore, toprovide a novel method and apparatus to reinforce thin wallthermoplastic storage vessels with one or more wraps of appliedcontinuous fiber.

[0006] It is still another object of the present invention to provide anovel method and apparatus to secure the applied fibers to the outersurface of a thin wall thermoplastic storage vessel so as to betterresist internal stress when the storage vessel is in use and preventdelamination when pressure is released.

[0007] Still another object of the present invention is to provide anovel method and apparatus for reinforcement of a thin wallthermoplastic storage vessel which includes a plurality of continuousjuxtapositioned fibers being reliably secured to the outer surface ofsaid storage vessel so as to be aligned in a predetermined spatialdirection resisting applied internal stress during vessel use.

[0008] These and still further objects of the present invention willbecome more apparent upon considering the following more detaileddescription of the present invention.

SUMMARY OF THE INVENTION

[0009] It has now been discovered by the present applicant that acontemporaneous pressurization of the internal cavity in a thin wallthermoplastic storage vessel while the applied reinforcement fibers onthe outer surface of said storage vessel are being thermally bondedthereto overcomes the problem previously experienced with inadequatejoinder of said reinforcement means. The internally applied pressure isseen to avert buckling or wrinkling of the thin storage vessel wallwhile being heated sufficiently for joinder between the reinforcementfibers and the outer vessel surface thereby enabling a sufficientbonding action therebetween. Internal pressurization of the storagevessel can thereafter be discontinued in the present reinforcementmethod allowing the fiber wrapped storage vessel to cool upontermination of said thermal bonding action. Accordingly, the presentmethod to reinforce said type thin wall hollow storage vessel compriseswrapping a plurality of continuous juxtapositioned reinforcement fibersformed with a material composition selected from the group consisting ofceramics, metals, carbon, glass compositions and organic polymers whilein an unbonded condition about the outer surface of said storage vessel,heating the outer vessel surface sufficiently to cause thermal bondingbetween the reinforcement fibers and said outer fiber wrapped vesselsurface, contemporaneously pressurizing the interior cavity of saidrotating fiber wrapped storage vessel with a coolant medium during saidheating step, and allowing the fiber wrapped storage vessel to cool uponterminating said heating step before discontinuing pressurization of thevessel interior cavity. Various liquid or gaseous coolants can beemployed in the present method to include water, air, nitrogen or thelike, while removal of said coolant medium from the storage vessel afterbeing heated during the present thermal bonding step can assist finalcooling of said reinforcement fiber wrap vessel. Thermal bonding in thepresent method involves some melting of the thermoplastic material beingemployed so that melting of the thermoplastic outer vessel surfaceoccurs which can be accompanied by melting of a thermoplastic matrixincluded in the applied fiber reinforcement. Accordingly, a softening ormelting action takes place during the present thermal bonding stepbetween the outer surface of the thermoplastic storage vessel and anythermoplastic polymer materials serving as the matrix composition inselected preformed tape embodiments having the continuous reinforcementfibers thereafter becoming permanently bonded therein.

[0010] The herein defined fiber reinforcement method understandablyenables a wide variety of fiber materials to be selected as previouslypointed out. Thus a reinforcement fiber material can be selected fromthe aforementioned class of suitable materials so long as it ismechanically stiffer than the selected thermoplastic vessel polymer andhas a glass transition or melting temperature higher than the surfacetemperature of the thermoplastic vessel during use. Selected polymerfibers can understandably include continuous bare filaments andcommingled continuous fibers which can be wetted by polymer melt flow inthe above described heat bonding procedure. For selection of a suitablepreformed continuous fiber material or prepreg tape having a matrixformed with a thermoplastic polymer, said matrix polymer is desirablychosen to have a softening or melt temperature equal to or lower thanthe softening temperature of the selected vessel polymer. Any suitableheating source can be used in the present method to reliably bond theapplied fiber reinforcement to the outer thermoplastic vessel surface.Contemplated heat sources include but are not limited to inert gases,oxidizing gases and reducing gases, including mixtures thereof, infraredheating sources, such as infrared panels and focused infrared means,conduction heating sources such as heated rollers, belts and shoedevices, electrical resistance heating sources, laser heating sources,microwave heating sources. RF heating sources, plasma heating sourcesand ultrasonic heating sources. An external flame heating sourceprovides economical heating with high-energy densities and with the gasburner or burners being suitable designed so as to heat the outercircumference of the fiber wrapped thermoplastic vessel. In a preferredembodiment, the wrapped storage vessel is rotated about the selectedheat source while having the interior cavity of said storage vesselbeing subjected to a pressurized condition. The applied pressure candesirably produce some radial expansion of the storage vessel wallthereby further enhancing the thermal bonding action taking place. Theapplied pressurization can also be initiated prior to said heating stepin the present method with applied pressures of ten pounds per squareinch or more having been found effective.

[0011] The fiber alignment selected in the present method can also varywith the particular shape of the thermoplastic storage vessel beingreinforced in said manner. Thus, a cylindrical shaped thermoplasticwater heater can have one or more wraps of the reinforcement fibersaligned in a hoop or helical direction whereas a spherical thermoplasticstorage vessel for the same use can understandably be wrapped indifferent spatial directions. A means of preserving the fiber alignmentin the present method until the melted polymer in physical contacttherewith again becomes solid can require that said fibers be subjectedto appropriate applied mechanical force during the thermal bondingaction. Such manner of fiber placement can be carried out by employingexternal tension winding means to guide the fiber reinforcement whilebeing wound around the outer vessel surface. An alternate means forretaining the fiber alignment is a compaction roller to apply mechanicalpressure to the heated fiber and polymer materials while being bondedtogether. Use of a compaction roller in such fiber placement can applyan external compaction force with zero tension being applied if desiredalthough it is within contemplation of the present invention for bothforms of external mechanical energy to be employed together when foundbeneficial. Another advantage of compaction roller use is the ability toorient such means in any spatial direction enabling fiber placement at apredetermined fiber angle dictated by the contour of the particularstorage vessel being reinforced in said manner. Thus, a cylindricalshaped thermoplastic pressure vessel can have one or more wraps of thereinforcement fibers aligned in a hoop or helical direction whereas aspherical thermoplastic storage vessel for such use can be wrapped in adifferent spatial direction.

[0012] Following termination of said thermal bonding step in the presentmethod, the fiber wrapped storage vessel can be allowed to cool in theambient atmosphere. Such cooling can be carried out in various ways toinclude removal of any pressurization liquid or gas coolant heatedduring the thermal bonding procedure as well as actively cooling with anapplied coolant medium. The completed fiber reinforcement can now serveto enable sufficiently higher operating pressures in said storage vesselthan otherwise permissible. Employment of the present method upon anotherwise conventional thermoplastic pressure vessel having a closed endcylindrical configuration has produced this result. Additionally, anouter protection or decorative coating to include heat shrinkabletubing, wrap or extruded coatings and the like can be applied to saidfiber reinforced thermoplastic storage vessel in a conventional mannerfor protection of the fiber reinforcement from environmental ormechanical damage and/or corrosion.

BRIEF DESCRIPTION OF THE DRAWING

[0013]FIG. 1 is a block diagram illustrating successive processing stepswhich can be employed in carrying out the method of the presentinvention.

[0014]FIG. 2 is a side view for a representative thermoplastic storagevessel being reinforced according to the present invention.

[0015]FIG. 3 is a schematic side view for a representative fullyautomated apparatus carrying out the fiber reinforcement method of thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Referring to the drawings, FIG. 1 is a block diagramrepresentation illustrating the sequence of processing steps employedaccording to the present invention for fiber reinforcement of arepresentative thermoplastic storage vessel having a closed endcylindrical configuration. The depicted fiber reinforcement process 10employs a typical six inch diameter, thirty-two inch long thermoplasticliquid container 12 having a 0.14 inch wall thickness which has-one ormore wraps of the thermoplastic reinforcement fibers 14 helically woundabout the outer cylindrical surface of said storage vessel. One or moretie wraps 16 of said thermoplastic reinforcement fibers can also besubsequently applied in the hoop direction for the purpose of carryingthe radial stress in the cylindrical pressure vessel. Said fiber wrappedvessel 18 next undergoes thermal bonding of the applied fiberreinforcement to the outer vessel surface. In a preferred embodiment,the fiber wrapped vessel is rotated about its central axis 20 whileheating the outer vessel surface with a conventional heat source 22.Heating of the fiber wrapped vessel in said manner produces some meltingof the outer vessel surface which upon vessel cooling retains theoriginally applied spatial orientation of said fibers. During saidheating step the hollow interior cavity of said fiber wrapped storagevessel 18 is pressurized 24 by various means to avoid any significantwrinkling or collapse of the vessel wall that could understandably detera fully bonded condition for the applied fiber reinforcement. Internalpressurization of the storage vessel can be initiated before thermalbonding of the fiber reinforcement while thereafter being discontinuedwhen the thermal bonding step has been completed and the reinforcedstorage vessel then being allowed to cool 26. Terminating pressurizationof the storage vessel 28 can also be carried out in various ways. Tofurther illustrate a suitable vessel pressurization in the presentmethod, the interior cavity of the fiber wrapped storage vessel 18 canbe filled with a liquid coolant, such as water, glycol, alcohol and thelike before the above described heating step is begun as well asthereafter being removed from the storage vessel after becoming heatedduring said processing step. Alternately, the interior cavity of saidstorage vessel 28 can be actively cooled with a suitable gaseous coolantto include air, nitrogen or other inert gas while the thermal bondingstep is being carried out and with said cooling action beingdiscontinued when the reinforced storage vessel is thereafter allowed tocool. Active cooling of the fiber wrapped storage vessel in said mannerat a pressure of 10 PSI or more has been proven satisfactory in thepresent method.

[0017] As herein pointed out, the fiber direction of the underlyingfiber layers for the illustrated cylindrical storage vessel is directedprimarily by the ability of said reinforced storage vessel to withstandinternal fluid pressure when such vessel is put into service. It can bereadily be appreciated, however, that other storage vessels having adifferent shape, such as a sphere or entirely open-ended cylindricalshape, can have the fiber alignment in an overall hoop direction forbetter resistance to internal fluid pressures during use. Additionally,the continuous fiber reinforcement can be applied in the present methodby various means. A selected amount of tension can be exerted upon thecontinuous fibers when being applied to assist with retention of thepredetermined or juxtapositioned fiber angle with respect to the vessellongitudinal axis in the herein illustrated embodiment. Similarly, amechanical compaction force exerted upon said fibers during initialplacement or subsequent thermal bonding can be employed for thispurpose. A wide variety of thermoplastic polymers can also be selectedas the material of construction for storage vessel being reinforcedaccording to the present method. Suitable organic polymers include butare not limited to polyethylene such as high density polyethylene andmedium density polyethylene, polypropylene, polyphenylene sulfide,polyetherketoneketone, polyamide, polyamideimide and polyuvinylidenedifluoride. A similar wide variety of materials are found suitable asthe fiber reinforcement in the present method to again include but notbe limited to ceramics, metals, carbon aramid and other organic polymerfibers having softening temperatures above that of the storage vessel inuse and glass compositions such as E type and S type glasses. Moreover,said fiber materials can also be applied in various structural forms toinclude a parallel alignment of the bare fibers and conventional fibertapes having the continuous parallel oriented fibers bonded together ina thermoplastic polymer matrix. The optional use being made of tielayers 16 in the presently illustrated embodiment can also serve to helpretain the juxtapositioned spatial orientation of the applied fiberreinforcement when selected thermoplastic polymer materials beingemployed are not miscible during the heating step.

[0018]FIG. 2 is a side view for a representative thermoplastic storagevessel being reinforced according to the present invention. Moreparticularly, the depicted cylindrical thermoplastic storage vessel 30is repeatedly illustrated during each processing step described in thepreceding preferred embodiment. As shown, said storage vessel 30comprises an elongated thermoplastic cylinder 32 having a closed end 34and an open end 36 fitted with a conventional inlet coupling 38. Thereis next depicted the manner whereby the continuous reinforcement fiber40 having a thermoplastic resin binder is deposited on the outer surface42 of the rotating thermoplastic storage vessel in a conventional helixpattern 44 while also being subjected to a tensile force being appliedin further customary manner. The next processing step being illustrateddepicts further rotation of the fiber wrapped storage vessel 46 whileadditional fiber wraps 48 are applied in a hoop direction enablingbetter retention of the underlying reinforcement fiber 40. The stillfurther depicted processing steps in the herein illustrated method offiber reinforcement demonstrate the heating step being employed to causethermal bonding between the applied unbonded reinforcement fibers andthe outer surfaces of said storage vessel. In doing so, a conventionalheat source 50 positioned in relatively close proximity to said fiberwrapped storage vessel 46 supplies the needed thermal energy during saidbonding procedure and which is further accompanied by having theinterior cavity 52 of said pressurized fiber wrapped storage vesselcooled with a selected liquid cooling medium 54 while said thermalbonding step is being carried out. Following said latter procedure, thereinforced storage vessel 56 is allowed to cool in the ambientatmosphere which further includes removal of the cooling fluid aftersufficient time has elapsed for resolidification of the polymersthermally bonded together.

[0019]FIG. 3 depicts a representative fully automated apparatus toconduct the required thermal bonding procedure according to the presentinvention. More particularly, apparatus 60 includes structural supportmeans 62 enabling rotation of an already fiber wrapped storage vessel 46in the ambient atmosphere. Motor driven releasable support members 64and 66 disposed at both ends of the supported vessel respond to commandsprovided with a conventional program controller 68 or equivalent dataprocessor, such as a software programmed computer. Said control means ispreprogrammed to automatedly start and stop all operations required inthe present thermal bonding procedure responsive to the given commands.Accordingly, the preprogrammed instructions are provided to said programcontroller for automated operation of all component mechanismsincorporated in the depicted apparatus according to a predeterminedsequence. Supply means providing suitable liquids and gases to thesuspended vessel during the thermal bonding procedure are furtherincluded in the depicted apparatus. Gas inlet 70 is connected to thesuspended vessel via a conventional flow valve 72 for this purpose as issimilarly connected liquid inlet 74. Still further included componentmechanisms in the depicted apparatus include electrical supply 76,natural gas supply 78, liquid and gas coupler member 80, connected toinlet vessel fitting 82 and a liquid drain member 84 also connected tothe suspended vessel 46. Natural gas fired burner 86 is positioned inclose proximity to the suspended vessel and is supplied from gas inlet78. While not shown in the present drawing, conventional motorizedvariable speed drive means connected to suspended vessel 46 can befurther included in the present apparatus for rotational speed variationwhen reinforcing different vessel sizes and shape in accordance with thepresent invention.

[0020] In fully automated operation, the FIG. 3 apparatus follows aprogrammed sequence of procedures responsive to the given commands ofprogram controller 68. Such operational sequence commences with thealready fiber wrapped storage vessel 46 being clamped between supportmembers 64 and 66 for vessel rotation while further sealing the vesselinlet opening 82. The suspended vessel is next internally pressurizedwith said instruction program to a preprogrammed pressure aboveatmosphere pressure with a suitable gaseous medium such as air and thelike. The now internally pressurized vessel is then instructed with saidprogram to rotate at a preprogrammed rotational speed. While continuingvessel rotation, gas fired burner 86 is next actuated for apreprogrammed time period again with said instruction program tocommence external heating of the vessel outer surface. As can be seen inthe FIG. 3 drawing, the illustrated burner configuration enables bothdome ends of the rotating fiber wrapped vessel to be heated concurrentlywith the central vessel region. A suitable liquid coolant, such as awater spray is also admitted to the hollow rotating vessel for apreprogrammed time period during the preprogrammed heating cycle. Suchcontemporaneous cooling means is provided to the vessel from inlet 74via flow valve 72 and rotary coupler 80. The vessel end of liquid drainmember 84 is next inserted into the hollow vessel cavity again pursuantto the automated instruction program while thereafter allowing theadmitted coolant to be subsequently removed. Automated retraction ofsaid drain member proceeds while the fiber wrapped storage vessel isbeing allowed to cool in the ambient atmosphere. Internal pressurizationof the vessel is not relieved with the programmed instruction untilsufficient vessel cooling has occurred. Said instruction program canstill further include automated final release of the processed vesselfrom the present apparatus after vessel rotation has been terminated.

[0021] The above described apparatus enables fiber reinforcement ofvarious cylindrical thin wall thermoplastic storage vessels in asignificantly improved manner. Limited external heating of the fiberwrapped vessel in the present apparatus can be expected to produce asuperior final product in several respects. Since only the outer surfaceof the underlying storage vessel undergoes any melting in the presentapparatus for satisfactory thermal bonding of the reinforcement fiber tothe outer wall surface, the original physical and chemicalcharacteristics of the underlying vessel polymer remain substantiallyunchanged. It is well recognized that polymer melting can produceserious defects in the resolidified polymer including thermaldegradation of the material itself as well as contributing to anincreased thermally induced residual stress condition. Contemporaneousliquid cooling of the inner vessel cavity while thermal bonding theapplied fiber reinforcement to the outer vessel wall surface in thepresent apparatus is carried out further helps keep the vessel polymerunmelted. Still further, retaining internal pressurization of the fiberwrapped vessel in the present apparatus until the vessel has cooledpromotes greater fiber bonding in the final product.

[0022] It will be apparent from the foregoing description that a broaduseful and novel method and apparatus has been provided to a reinforcethin wall thermoplastic storage vessel with one or more wraps of appliedcontinuous fiber. It will be apparent, however, that variousmodifications can be made in the disclosed process and apparatus withoutdeparting from the spirit and scope of the present invention. Forexample, it is contemplated that some heating of the unbondedreinforcement when being initially applied to the outer surface of thestorage vessel can assist in having the fiber conform more closely tothe particular contours of the vessel surface. Likewise, it iscontemplated that other organic polymers, other vessel shapes and otherprocessing equipment configurations than herein specifically disclosedcan be substituted in carrying out the present method. Consequently, itis intended to cover all variations in the disclosed reinforcementmethod and apparatus which may be devised by persons skilled in the artas falling within the scope of the appended claims.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:
 1. An apparatus to mechanically reinforce a cylindricalshaped hollow thin wall thermoplastic storage vessel having an open endwith at least one wrap of continuous reinforcement fiber employing athermoplastic resin binder, said fiber reinforcement having beenhelically wrapped about the outer surface in an unbonded condition,which comprises: (a) physical support means disposed at the vessel endsto rotate the fiber wrapped storage vessel when suspended in the ambientatmosphere, (b) external heating means to thermally bond the fiberreinforcement to the outer surface of said suspended storage vesselwhile rotating in the ambient atmosphere, (c) external gaseous means tointernally pressurize the hollow inner cavity of the suspended rotatingstorage vessel while thermal bonding of the fiber reinforcement occursin the ambient atmosphere, (d) external liquid cooling means tocontemporaneously cool the hollow inner cavity of the suspended rotatingstorage vessel while said thermal bonding of the fiber reinforcementoccurs, and (e) automated electrical control means in said apparatusenabling such fiber reinforcement procedure to be carried out in acontinuous sequential manner.
 2. The apparatus of claim 1 wherein theautomated electrical control means includes a preprogrammed controller.3. The apparatus of claim 2 wherein the preprogrammed controllercomprises a software programmed computer.
 4. The apparatus of claim 1wherein the reinforcement fiber is selected from the group consisting ofceramics, metals, carbon, glass compositions and organic polymers. 5.The apparatus of claim 1 wherein the fiber reinforcement includes fiberwrapped in the hoop direction.
 6. The apparatus of claim 1 whereinmultiple wraps of the fiber reinforcement are employed.
 7. The apparatusof claim 1 wherein internal pressurization of the fiber reinforcedstorage vessel is not discontinued until said storage vessel has cooled.8. The apparatus of claim 7 wherein removal of the liquid coolantprecedes discontinuation of the internal vessel pressurization.
 9. Theapparatus of claim 8 wherein removal of the liquid coolant is conductedwith vessel outlet drain means.
 10. The apparatus of claim 1 wherein asupport member disposed at the open end of the suspended storage vesselincludes rotary coupler means admitting both gaseous and liquid mediumsto the hollow cavity of the storage vessel.
 11. The apparatus of claim 1wherein gas fired burner means are employed to thermally bond the fiberreinforcement.
 12. The apparatus of claim 1 wherein the physical supportmeans further includes a motorized variable speed drive mechanism.